1. Field of the Invention
The present invention relates to controller units that prevent wrong attachment of modules in the case where a plurality of types of modules are to be attached to a base unit.
2. Description of the Related Art
The controller units are what is called programmable logic controllers (PLCs), which are control devices that sequentially perform the steps of control in predetermined order or according to predetermined procedures. For example, a safety door is installed around a machine tool that machines workpieces. The safety door is installed to separate the operator from the machine tool to ensure operator's safety. A machining start button for starting machining of the machine tool may be provided at a position slightly away from the safety door, and an emergency stop button may be provided next to the machining start button. The safety door may be provided with a limit switch that detects if the safety door is open or closed. The machine tool may be provided with a predetermined sensor that detects completion of machining.
In this case, the controller unit receives a signal from the limit switch, a signal from the machining start button, a signal from the emergency stop button, and a signal from the predetermined sensor, and outputs an operation start control signal that starts operation of the machine tool and an operation stop control signal that stops operation of the machine tool. The controller unit performs the steps of control (e.g., starts operation of the machine tool, and stops operation of the machine tool if it detects completion of machining) only if it detects a predetermined order (e.g., if it detects that the machining start button is turned on after the safety door is closed). For example, if the machine tool is in operation when the controller unit detects depression of the emergency stop button or detects that the safety door is opened, the controller unit stops the machine tool.
The controller unit includes a base unit and modules. Each module includes a printed circuit board and a casing having the printed circuit board mounted therein. The base unit has slots or spaces where the modules are to be mounted. A plurality of types of modules are mounted in the slots of the base unit. Each module is mounted by fitting a pair of male and female connectors together. One of the connectors is included in the base unit, and the other is included in the module. The types of modules include a power supply module, a central processing unit (CPU) module, a communication module, an input module, an output module, etc.
Mounting a wrong type of module on a base unit can cause breakdown of an electronic circuit component mounted on the printed circuit board of the module. The modules are mounted on the base unit by connecting the connectors together, but signals connected to the module and their arrangement vary depending on the type of module. Accordingly, the type of module to be mounted in each slot is decided in advance. In order to avoid electrical failure resulting from mounting of a wrong module, the size (number of pins) of connectors or the attached positions of the connectors are varied depending on the type of module, and this variation provides a structure for preventing wrong insertion. For example, if the power supply module and another module are switched and the power supply module is mounted in the slot of the base unit in which the module other than the power supply module is supposed to be mounted, an excessive voltage is applied to the electronic circuit component of this module, which may result in breakdown of the electronic circuit component. Various proposals are conventionally made in order to prevent wrong mounting of modules. See, e.g., Japanese Utility Model Application Publication No. H04-55184 (JP H04-55184 Y) and Japanese Patent Application Publication No. 2009-276894 (JP 2009-276894 A).
One of methods for mounting a module to a base unit is to provide a detachable turning support configuration between the base unit and the module and turn the module with respect to the base unit so that a connector included in the module is fitted to a connector included in the base unit.
In the above mounting methods that are conventionally proposed in order to prevent wrong attachment, the module is not turned but is linearly pressed into the slot in order to attach the module to the base unit. In the method in which the module is turned and attached to the base unit, the module is turned around a turning support. Accordingly, even a wrong module may be able to be fitted into the slot by the turning operation, even if not completely. Namely, a part of the connector of the wrong module may be able to be fitted to the connector of the base unit. If the operator thinks that the module just need be pressed harder to press the connector into the insertion hole, or the connector cannot be inserted smoothly because it is inserted slightly obliquely, etc. without being aware of the fact that he/she is trying to attach a wrong module, he/she may press the module too hard that the connector may be damaged. A proposal for effectively preventing wrong attachment is therefore desired even for the mounting method using turning of modules.